Stratigraphy and Palaeontology
Toran Khamoshi; Ahmad Lotfabad Arab; Mohammad Reza Vaziri
Abstract
In order to study the Lower Cretaceous deposits' coral fossils, the Baghin section was chosen and sampled. This section consists of a sequence of green marl, limestone and shaly limestone deposits. In this section, diverse groups of microfossils (orbitolinids, algae and ostracods) and macrofossils ...
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In order to study the Lower Cretaceous deposits' coral fossils, the Baghin section was chosen and sampled. This section consists of a sequence of green marl, limestone and shaly limestone deposits. In this section, diverse groups of microfossils (orbitolinids, algae and ostracods) and macrofossils (corals, echinoids, bivalves, brachiopods, gastropods,…) are present. The presence of diverse collection fossils, especially large orbitolinid foraminifera indicated a favorable environmental conditions and absence of planktonic foraminifera indicated shallow environmental conditions. Also, the presence of platycopid and podocopid ostracods and corals confirm the shallow, warm, light and suitable paleoecological conditions.
Stratigraphy and Palaeontology
Ahmad Lotfabad Arab
Abstract
In order to identify, classify and paleoecological study of Lower Cretaceous echinoid fauna in northwest of Kerman area, the stratigraphic section of Siriz, was selected and its specimens were sampled and studied. Echinoids were studied and identified from a rich and diverse collection of macrofossils ...
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In order to identify, classify and paleoecological study of Lower Cretaceous echinoid fauna in northwest of Kerman area, the stratigraphic section of Siriz, was selected and its specimens were sampled and studied. Echinoids were studied and identified from a rich and diverse collection of macrofossils (echinoids, brachiopods, bivalves, gastropods and corals) and microfossils (foraminifera and ostracods), which present in this deposits. Sixteen genera and species of echinoids are reported for the first time from the region, among which six species are new and reported from Kerman area previously. The co-existence of echinoids and other fossil groups in Siriz area confirms an Aptian age for the sediments. Also, it can be concluded that a shallow, less than 50 meters and warm platform environment was prevailed during the deposition of the strata.
Economic Geology
Zahra Akbari; ali yarmohammadi; Iraj rassa
Abstract
The Fe-Pb Ahangaran deposit, hosted by tuffaceous siltstone of the Early Cretaceous sedimentary sequence in the northern part of the Malayer-Esfahan Metallogenic Belt (MEMB), Iran. Ore mineralization occurred as stratiform and a widespread veinlet zone in the upper part of Lower Cretaceous terrigenous ...
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The Fe-Pb Ahangaran deposit, hosted by tuffaceous siltstone of the Early Cretaceous sedimentary sequence in the northern part of the Malayer-Esfahan Metallogenic Belt (MEMB), Iran. Ore mineralization occurred as stratiform and a widespread veinlet zone in the upper part of Lower Cretaceous terrigenous unit (Kc). Four different ore types can be distinguished in deposit include: (1) veinlet (feeder) zone, (2) sulfide-Fe- oxide stratiform ore (3) barite ore and (4) vein ore. Ore minerals in the different ore types are pyrite, siderite, magnetite, galena, barite, chalcopyrite and tetrahedrite and rare minerals are pyrrhotite, arsenopyrite, and freibergiteCarbonatization and silicification are the main hydrothermal alterations in this deposit. The orebodies in the Ahangaran deposit have been replaced by iron oxide minerals in supergene process and have been formed a thick gossan zone. The textural and mineralogical data provide evidence of three stages of mineralization (Early, main and late stage) in Ahangaran deposit. According to evidences such as tectonic setting, type of host rock, geometry of deposit, sulfide-Fe oxide ore types, textures and structures indicate that the Ahangaran deposit is compatible with a sub-seafloor replacement mineralization that has been suggested for some Sedex deposits.
Z. latifi; F. Foroughi; M. Motamedalshariati; S. N. Raeisossadat
Abstract
Calcareous nannofossils of Nimbolook section in north west of Qayen, east of Iran have been investigated. The section is 164 m thick and consists of limestone, marlstone and shale. Seventy six nannofossil species belong to thirty genera from fifteen families were identified. Based on the identified calcareous ...
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Calcareous nannofossils of Nimbolook section in north west of Qayen, east of Iran have been investigated. The section is 164 m thick and consists of limestone, marlstone and shale. Seventy six nannofossil species belong to thirty genera from fifteen families were identified. Based on the identified calcareous nannofossils, a part of subzone CC7b and biozone CC8 and a part of biozone CC9 of Sissingh biozonation (1977) and a part of subzone NC7 and biozones NC8, NC9 and a part of biozone NC10 of Roth biozonation (1978) have been suggested for the Nimbolook section. Therefore, an age of late Aptian–Albian and early Cenomanian? is assigned to the deposits of this section.
M Boveiri Konari; E Rastad; M Rastad; A Nakini; M Haghdoost
Abstract
Tappehsorkh Zn-Pb-(Ag) deposit, hosted by Lower Cretaceous siltstone, tuff and dolomite, is located in the northern part of the Irankuh mountain range, south of Esfahan. Sulphides in this ore have a relatively simple mineralogy including sphalerite, galena, tetrahedrite, pyrite and to a lesser extent, ...
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Tappehsorkh Zn-Pb-(Ag) deposit, hosted by Lower Cretaceous siltstone, tuff and dolomite, is located in the northern part of the Irankuh mountain range, south of Esfahan. Sulphides in this ore have a relatively simple mineralogy including sphalerite, galena, tetrahedrite, pyrite and to a lesser extent, chalcopyrite, marcasite and bornite. Gangue minerals are predominantly dolomite, quartz and barite. Based on zoning in the sulphide mineralization, texture and structure and location of ore facies relative to syn-sedimentary normal faults, theses ore facies are classified as vein-veinlet, laminated and massive. Dolomitic-silicic alteration is among the major processes concomitant with sulphide mineralization. The greatest degrees of alteration and related ore mineralization occur at the vicinity of the normal faults and decrease away from it. Geochemical studies indicate that the ore-bearing fluids were of oxidized composition, which were reduced once reaching favorable host rocks and consequently deposited sulphide minerals. Minor and trace element studies in the various sulfide ore facies demonstrate that the ore-bearing fluid in all the ore facies has a similar composition. Textures such as framboidal pyrite, contemporaneous folding of organic matter along with sulphide lamination in the laminated ore facies, and diagenetic structures such as load casts in the host siltstone indicate that sulphide mineralization has occurred in the sedimentary-diagenetic stage. However, sulphide mineralization in the regional dolomite is considered to have occurred in a shallow diagenetic environment because of replacement of regional dolomite by hydrothermal dolomite. Based on features of ore mineralization such as the extensional tectonic setting, siltstone and carbonate host rocks, and occurrence of various sulphide facies such as vein-veinlet, laminated and massive, the Tappehsorkh deposit is very similar to Sedex-type deposits.
M Boveiri Konari; E Rastad; N Rashidnejad-Omran
Abstract
Lower Cretaceous volcano-sedimentary sequence in the northwest and southeast of Safashahr (Dehbid) in marginal subzone of southern Sanandaj-Sirjan Zone comprises the Keshtmahaki deposit and few other occurrences of copper (-silver). The oldest rock units in the region are Jurassic shale and sandstone, ...
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Lower Cretaceous volcano-sedimentary sequence in the northwest and southeast of Safashahr (Dehbid) in marginal subzone of southern Sanandaj-Sirjan Zone comprises the Keshtmahaki deposit and few other occurrences of copper (-silver). The oldest rock units in the region are Jurassic shale and sandstone, which are unconformably overlain by the Lower Cretaceous progressive sequence with basal conglomerate, sandstone and silty shale. Copper (-Ag) mineralization occurred in the Lower Cretaceous pyroclastics and volcanic lava. The host rock is a crystal lithic tuff with trachyandesite-andesite affinity in which the stratabound and lenticular ore body is extended discontinuously over 35 km that laterally and vertically changed into orbitolina limestone. Ore minerals include chalcocite, bornite, native copper, digenite, chalcopyrite, pyrite, Ag-bearing clausthalite, covellite, anilite, malachite and azurite. Ore textures and structures are open space filling, vein-veinlet, replacement, disseminated and laminated-like. The lithogeochemical studies in 6 lithostratigraphic profiles from NW to SE of Safashahr indicated Cu (-Ag) mineralization occurrence in a specific stratigraphic unit and a positive relationship with Zn. The lithological, mineralogical, lithogeochemical and microscopic investigations revealed that mineralization initially occurred contemporaneously with volcanism in volcano-sedimentary sequences (absorption of Cu by ferric hydroxide, clay minerals and replacement in feldspar lattice) and then in burial diagenesis during dehydration of pyroclastic and detrital units and alteration resulting from this hydrothermal fluid, Cu released and transported by hydrothermal diagenesis fluids. When this ore-bearing hydrothermal fluid received by the rock unit with high permeability (pyrite-bearing crystal lithic tuff) and reduced conditions resulted from abundance of pyite, replaced them as copper sulphide minerals. S isotopic data of sulphidic minerals indicated that the bacterially sulfate reduction of sea water as an important role provided the nessecary sulfur for sulfide mineralization. Geochemical features of volcanic and pyroclastic units indicated that they formed in an intra-arc rift. On the basis of this study and with respect to some evidences such as tectonic setting, host rock, lenticular shape of the ore body, structure and texture as well as mineral paragenesis we suggest that Keshtmahaki Cu (-Ag) mineralization and surrounding occurrences are Volcanic Red Bed (VRB) type deposit that formed and concentrated contemporaneously with submarine volcanism to deep burial diagenesis processes.
